Changes in body composition and energetic efficiency in response to growth curve and dietary energy-to-protein ratio in broiler breeders.

Body composition plays an important role in reproduction in broiler breeders. The aim of this study was to evaluate the dynamics in body composition and energetic efficiency in broiler breeders, using different dietary strategies. About 1,536-day-old pullets were randomly allotted to 24 pens in a 2 × 4 factorial design with 2 growth curves (standard or elevated (+15%)) and 4 diets, with a step-wise increment in energy (96, 100, 104, and 108% apparent metabolizable energy nitrogen corrected [AMEn]) fed on a pair-gain basis. Body composition was determined at 10 time points from 0 to 60 wk of age. Body protein mass was linearly related to body weight (BW) in growing breeders, which can be expressed as -6.4+0.184*BW (R2 = 0.99; P < 0.001). Body fat mass was exponentially related to BW in growing breeders, which can be expressed as -42.2+50.8*1.0006BW (R2 = 0.98; P < 0.001). A higher energy-to-protein ratio resulted in higher body fat mass at the same BW (P < 0.001). Sexual maturation was related to body protein mass at 21 wk of age, where each 100 g of body protein mass extra advanced sexual maturation by 5.4 d (R2 = 0.83). Estimates of energetic efficiency for growth (kg) and egg production (ke) appeared not constant, but varied with age in a quadratic manner between 0.27 and 0.54 for kg and between 0.28 and 0.56 for ke. The quadratic relationship could be expressed as kg=0.408-0.0319*Age+0.00181*Age2 (R2 = 0.72; P < 0.001) and ke=-0.211+0.034*Age-0.00042*Age2 (R2 = 0.46; P < 0.001). Body protein mass in broiler breeders is tightly regulated and mainly depended on BW and seems to be the main determinant for sexual maturation. Body fat mass is exponentially related to BW, where an increase in dietary energy-to-protein ratio results in a higher body fat mass. Treatments had minimal effects on estimated energetic efficiencies in breeders.

Mucosal expression of Ca and P transporters and claudins in the small intestine of broilers is altered by dietary Ca:P in a limestone particle size dependent manner.

High calcium (Ca) intake and fine limestone reduces precaecal phosphorus (P) absorption independently of P solubility in broilers. This study aimed to determine whether dietary total Ca: total P ratio (Ca:P) and limestone particle size (LPS) affect gene expression of P transporters in the small intestine. A total of 384 one-day-old Ross 308 male broiler chickens received diets low (0.50), medium (1.00) or high (1.75) in Ca:P containing either fine (160 µm) or coarse (1062 µm) limestone, in a 3×2 factorial arrangement. Expression of Ca- and P-related genes were determined using real-time quantitative PCR (RT-qPCR) in duodenum and jejunum. Increasing dietary Ca:P decreased duodenal calcium-sensing receptor (CaSR), calbindin-D28k (CaBP-D28k), plasma membrane Ca-ATPase 1 (PMCA1) and sodium-coupled P cotransporter type IIb (NaPi-IIb), but not transient receptor potential canonical 1 (TRPC1) mRNA. This effect was greater with fine limestone when Ca:P increased from low to medium, but greater with coarse limestone when increased from medium to high. A similar inhibitory effect was observed for jejunal CaBP-D28k expression where increasing dietary Ca:P and fine limestone decreased CaSR mRNA, while dietary Ca:P decreased TRPC1 mRNA only for coarse limestone. It also decreased jejunal NaPi-IIb mRNA irrespective of LPS. Dietary treatments did not affect jejunal PMCA1 mRNA expression or that of inorganic phosphate transporter 1 and 2 and xenotropic and polytropic retrovirus receptor 1 in both intestinal segments. Dietary Ca increase reduced mucosal claudin-2 mRNA in both segments, and jejunal zonula occludens-1 (ZO-1) mRNA only for coarse limestone. In conclusion, increasing dietary Ca:P reduced expression of duodenal P transporters (NaPi-IIb) in a LPS dependent manner, hence Ca induced reduction in intestinal P absorption is mediated by decreasing P transporters expression. Dietary Ca reduces Ca digestibility by downregulating mRNA expression of both Ca permeable claudin-2 and Ca transporters (CaBP-D28k, PMCA1).

Impact of growth curve and dietary energy-to-protein ratio of broiler breeders on offspring quality and performance.

The impact of growth curve (GC) and dietary energy-to-protein ratio of broiler breeder hens on chick quality and broiler performance was investigated. Pullets (n = 1,536) were randomly allotted to 24 pens and assigned to 1 of 8 treatments from hatch onwards, according to a 2 × 4 factorial arrangement with 2 GC (standard growth curve = SGC or elevated growth curve = EGC, +15%) and 4 diets, differing in energy-to-protein ratio (96%, 100%, 104%, and 108% AMEn diet). At 28 and 36 wk of age, 60 hatching eggs per maternal pen were selected for incubation and 768-day-old broilers were assigned to 32 pens according to maternal treatment. Broilers from EGC breeders were 1.9 g heavier at hatch (P < 0.001) and 36 g heavier at slaughter (P = 0.001) than broilers from SGC breeders due to a 1.0 g/d higher growth rate (P = 0.003) and 1.5 g/d higher feed intake (P = 0.006) from hatch to 32 d of age. An increase in breeder dietary energy-to-protein ratio resulted in a linear decrease in embryonic mortality in the first 3 d of incubation (ß = -0.2% per % AMEn; P = 0.05). At hatch, broiler BW decreased with an increasing breeder dietary energy-to-protein ratio (ß = -0.1 g per % AMEn; P = 0.001), whereas at slaughter broiler BW increased with an increasing breeder dietary energy-to-protein ratio (ß = 3.2 g per % AMEn; P = 0.02). This was due to a linear increase in growth rate (ß = 0.1 g/d per % AMEn; P = 0.004) and feed intake (ß = 0.1 g/d per % AMEn; P = 0.02). Additionally, an increase in breeder dietary energy-to-protein ratio resulted in a linear decrease in body weight corrected feed conversion ratio (ß = -0.002 per % AMEn; P = 0.002). Overall, it can be concluded that a higher GC of breeders and an increase in breeder dietary energy-to-protein ratio enhances offspring performance.

Impact of growth curve and dietary energy-to-protein ratio of broiler breeders on egg quality and egg composition.

Egg characteristics have an impact on embryonic development and post-hatch performance of broilers. The impact of growth curve (GC) and dietary energy-to-protein ratio of broiler breeder hens on egg characteristics was investigated. At hatch, 1,536 pullets were randomly allotted to 24 pens in a 2 × 4 factorial dose-response design with 2 GC (standard growth curve = SGC or elevated growth curve = EGC (+ 15%)) and 4 diets, differing in energy-to-protein ratio (defined as 96%, 100%, 104% and 108% AMEn diet). Feed allocation per treatment was adapted weekly to achieve the targeted GC and to achieve pair-gain of breeders within each GC. Breeders on an EGC produced larger eggs (∆ = 2.3 g; P < 0.001) compared to breeders on a SGC. An exponential regression curve, with age (wk) of the breeders, was fitted to describe the impact of GC and dietary energy-to-protein ratio on egg composition. Yolk weight was 0.8 g higher for eggs from EGC breeders than from SGC breeders (a-108.1*0.907Age, where a was 22.1 and 22.9 for SGC and EGC, respectively; R2 = 0.97; P<0.001). An interaction between GC and dietary energy-to-protein ratio on albumen weight was observed (P = 0.04). Dietary energy-to-protein ratio did not affect albumen weight in SGC breeders (42.7-56.2*0.934Age; R2 = 0.89), but for EGC breeders, a higher dietary energy-to-protein ratio resulted in a 0.9 g lower albumen weight from 96% AMEn to 108% AMEn (a-62.9*0.926Age, where a was 43.4, 43.2, 42.8, and 42.5 for 96% AMEn, 100% AMEn, 104% AMEn, and 108% AMEn, respectively; R2 = 0.86). Albumen DM content decreased linearly with an increased dietary energy-to-protein ratio, but this was more profound in EGC breeders (ß = -0.03 %/% AMEn) than in SGC breeders (ß = -0.01 %/% AMEn; P = 0.03). Overall, it can be concluded that an EGC for breeders led to larger eggs with a more yolk and albumen, whereas dietary energy-to-protein ratio had minor effects on egg composition.

Impact of growth curve and dietary energy-to-protein ratio on productive performance of broiler breeders.

The impact of growth curve (GC) and dietary energy-to-protein ratio on productive performance of broiler breeder females was investigated from 0 to 60 wk of age. One-day-old pullets (n = 1,536) were randomly allotted to 24 pens according to a 2 × 4 factorial arrangement, with 2 GC (standard growth curve = SGC or elevated growth curve = EGC, +15%) and 4 diets, differing in energy-to-protein ratio (96%, 100%, 104%, or 108% AMEn). Feed allocation per treatment was adapted weekly based on the desired GC, meaning that breeders fed the different diets within each GC were fed according to a paired-gain strategy. Linear and quadratic contrasts for energy-to-protein ratio for each GC were evaluated. Elevated growth curve breeders had an earlier sexual maturity (∆ = 4.1 d) than SGC breeders. Egg weight was higher for EGC breeders (∆ = 2.3 g) than for SGC breeders over the whole laying phase (22-60 wk). No differences between EGC and SGC breeders were observed on settable egg production. An increase in dietary energy-to-protein, at a similar BW, led to a linear increase in age at sexual maturity (ß = 0.14 d/% AMEn). From 22 to 40 wk of age, an increase in dietary energy-to-protein ratio led to a linear decrease in egg weight (ß = -0.06 g/% AMEn), regardless of GC. An interaction between GC and dietary energy-to-protein ratio was observed on settable egg production in this phase. An increase in dietary energy-to-protein ratio led to a linear decrease on settable egg production, which was more profound in EGC breeders (ß = -0.70 eggs/% AMEn) than in SGC breeders (ß = -0.19 eggs/% AMEn). From 41 to 60 wk of age, an interaction between GC and dietary energy-to-protein ratio was observed on egg weight. In the EGC, an increase in dietary energy-to-protein ratio led to a linear decrease in egg weight (ß = -0.13 g/% AMEn), whereas in the SGC, a linear increase in egg weight was observed (ß = 0.03 g/% AMEn). From 41 to 60 wk of age, no differences between diets were observed on settable egg production. It can be concluded that a higher GC of breeders has beneficial effects on egg weight, while maintaining settable egg production. Feeding breeders a lower dietary energy-to-protein ratio stimulated productive performance of broiler breeder hens, mainly during the first phase of lay. This effect was more profound when breeders were fed according to a higher GC.

Coarse limestone does not alleviate the negative effect of a low Ca/P ratio diet on characteristics of tibia strength and growth performance in broilers.

The hypothesis was tested that an increased digestion of coarse compared with fine limestone can alleviate the negative effects of a low dietary Ca/P ratio on the growth performance and characteristics of tibia strength (CTS) in broilers. A total of 1,152 Ross 308 broiler chickens received a standard commercial starter feed from day 0 to 13. From day 14 onward, birds received 1 of 12 diets containing 1 of 6 Ca/P ratios (0.50, 0.75, 1.00, 1.25, 1.50, and 1.75) and 1 of 2 limestone particle sizes (<500 [fine] and 500 to 2,000 [coarse] µm) in a study with a 6 × 2 factorial arrangement of treatments. Total P content was fixed at 5.5 g/kg for all treatment diets. Each treatment was replicated 6 times with 16 birds per replicate pen. On day 20 and 21, twelve birds per pen were randomly selected from 4 of the 6 replicate pens for tibia analysis and digesta collection from different gut segments. The apparent Ca digestibility was higher for fine than coarse limestone in the jejunum (P = 0.043). However, this difference in Ca digestibility disappeared for the low, whereas it remained for the high Ca/P ratios in the proximal (Pinteraction = 0.067) and distal (Pinteraction = 0.052) ileum. In addition, coarse limestone improved apparent P digestibility in the proximal and distal ileum (P < 0.001) but not in the jejunum (P = 0.305). Regardless of limestone particle size, reducing dietary Ca/P ratio linearly improved apparent Ca and P digestibility in the proximal and distal ileum (P < 0.001). Moreover, decreasing dietary Ca/P ratio linearly (P < 0.001) and quadratically (P < 0.046) reduced the CTS. Reducing dietary Ca/P ratio linearly (P < 0.003) and quadratically (P ≤ 0.006) decreased body weight gain and increased feed conversion ratio. For both fine and coarse limestone, the optimal Ca/P ratio was 1.00 to 1.25 to optimize apparent Ca and P digestibility while maintaining growth performance and CTS. Reducing Ca/P ratio from 1.75 to 1.00 improved distal ileal Ca and P apparent digestibility from 36.6 to 53.7% and 48.0 to 58.3%, respectively. In conclusion, coarse limestone is equally digestible with fine limestone at a low Ca/P ratio but is less digestible at a high Ca/P ratio, and the optimal Ca/P ratio in the diet is 1.00 to 1.25 for both fine and coarse limestone.